|
Server : Apache/2.2.2 (Fedora) System : Linux App1.pathumtani.go.th 2.6.20-1.2320.fc5smp #1 SMP Tue Jun 12 19:40:16 EDT 2007 i686 User : apache ( 48) PHP Version : 5.2.9 Disable Function : NONE Directory : /proc/self/root/usr/share/doc/postgresql-8.1.9/html/ |
Upload File : |
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>Rules and Privileges</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REV="MADE"
HREF="mailto:pgsql-docs@postgresql.org"><LINK
REL="HOME"
TITLE="PostgreSQL 8.1.9 Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="The Rule System"
HREF="rules.html"><LINK
REL="PREVIOUS"
TITLE="Rules on INSERT, UPDATE, and DELETE"
HREF="rules-update.html"><LINK
REL="NEXT"
TITLE="Rules and Command Status"
HREF="rules-status.html"><LINK
REL="STYLESHEET"
TYPE="text/css"
HREF="stylesheet.css"><META
HTTP-EQUIV="Content-Type"
CONTENT="text/html; charset=ISO-8859-1"><META
NAME="creation"
CONTENT="2007-04-20T04:40:08"></HEAD
><BODY
CLASS="SECT1"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="5"
ALIGN="center"
VALIGN="bottom"
>PostgreSQL 8.1.9 Documentation</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="rules-update.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="rules.html"
>Fast Backward</A
></TD
><TD
WIDTH="60%"
ALIGN="center"
VALIGN="bottom"
>Chapter 34. The Rule System</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="top"
><A
HREF="rules.html"
>Fast Forward</A
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="top"
><A
HREF="rules-status.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="RULES-PRIVILEGES"
>34.4. Rules and Privileges</A
></H1
><A
NAME="AEN34335"
></A
><A
NAME="AEN34338"
></A
><P
> Due to rewriting of queries by the <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
rule system, other tables/views than those used in the original
query get accessed. When update rules are used, this can include write access
to tables.</P
><P
> Rewrite rules don't have a separate owner. The owner of
a relation (table or view) is automatically the owner of the
rewrite rules that are defined for it.
The <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> rule system changes the
behavior of the default access control system. Relations that
are used due to rules get checked against the
privileges of the rule owner, not the user invoking the rule.
This means that a user only needs the required privileges
for the tables/views that he names explicitly in his queries.</P
><P
> For example: A user has a list of phone numbers where some of
them are private, the others are of interest for the secretary of the office.
He can construct the following:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TABLE phone_data (person text, phone text, private boolean);
CREATE VIEW phone_number AS
SELECT person, phone FROM phone_data WHERE NOT private;
GRANT SELECT ON phone_number TO secretary;</PRE
><P>
Nobody except him (and the database superusers) can access the
<TT
CLASS="LITERAL"
>phone_data</TT
> table. But because of the <TT
CLASS="COMMAND"
>GRANT</TT
>,
the secretary can run a <TT
CLASS="COMMAND"
>SELECT</TT
> on the
<TT
CLASS="LITERAL"
>phone_number</TT
> view. The rule system will rewrite the
<TT
CLASS="COMMAND"
>SELECT</TT
> from <TT
CLASS="LITERAL"
>phone_number</TT
> into a
<TT
CLASS="COMMAND"
>SELECT</TT
> from <TT
CLASS="LITERAL"
>phone_data</TT
> and add the
qualification that only entries where <TT
CLASS="LITERAL"
>private</TT
> is false
are wanted. Since the user is the owner of
<TT
CLASS="LITERAL"
>phone_number</TT
> and therefore the owner of the rule, the
read access to <TT
CLASS="LITERAL"
>phone_data</TT
> is now checked against his
privileges and the query is permitted. The check for accessing
<TT
CLASS="LITERAL"
>phone_number</TT
> is also performed, but this is done
against the invoking user, so nobody but the user and the
secretary can use it.</P
><P
> The privileges are checked rule by rule. So the secretary is for now the
only one who can see the public phone numbers. But the secretary can setup
another view and grant access to that to the public. Then, anyone
can see the <TT
CLASS="LITERAL"
>phone_number</TT
> data through the secretary's view.
What the secretary cannot do is to create a view that directly
accesses <TT
CLASS="LITERAL"
>phone_data</TT
>. (Actually he can, but it will not work since
every access will be denied during the permission checks.)
And as soon as the user will notice, that the secretary opened
his <TT
CLASS="LITERAL"
>phone_number</TT
> view, he can revoke his access. Immediately, any
access to the secretary's view would fail.</P
><P
> One might think that this rule-by-rule checking is a security
hole, but in fact it isn't. But if it did not work this way, the secretary
could set up a table with the same columns as <TT
CLASS="LITERAL"
>phone_number</TT
> and
copy the data to there once per day. Then it's his own data and
he can grant access to everyone he wants. A
<TT
CLASS="COMMAND"
>GRANT</TT
> command means, <SPAN
CLASS="QUOTE"
>"I trust you"</SPAN
>.
If someone you trust does the thing above, it's time to
think it over and then use <TT
CLASS="COMMAND"
>REVOKE</TT
>.</P
><P
> This mechanism also works for update rules. In the examples of
the previous section, the owner of the tables in the example
database could grant the privileges <TT
CLASS="LITERAL"
>SELECT</TT
>,
<TT
CLASS="LITERAL"
>INSERT</TT
>, <TT
CLASS="LITERAL"
>UPDATE</TT
>, and <TT
CLASS="LITERAL"
>DELETE</TT
> on
the <TT
CLASS="LITERAL"
>shoelace</TT
> view to someone else, but only
<TT
CLASS="LITERAL"
>SELECT</TT
> on <TT
CLASS="LITERAL"
>shoelace_log</TT
>. The rule action to
write log entries will still be executed successfully, and that
other user could see the log entries. But he cannot create fake
entries, nor could he manipulate or remove existing ones.</P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="rules-update.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="rules-status.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Rules on <TT
CLASS="COMMAND"
>INSERT</TT
>, <TT
CLASS="COMMAND"
>UPDATE</TT
>, and <TT
CLASS="COMMAND"
>DELETE</TT
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="rules.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Rules and Command Status</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>